Outdoor electrical power terminals filled with silicon oil are conventionally used in connection with high voltage cables, such as cables carrying 170 kV or greater voltage. However, there is a risk that the silicon oil may leak out of the power terminal and cause a power failure. Furthermore, since the power terminal is often mounted high above the ground, it can be difficult to monitor the power terminal for any leaking silicon oil before the power terminal fails.
Generally these conventional power terminals employ a silicon oil sensor having a conductive layer directly formed by conductive particles or a porous material (e.g. polytetrafluoroethylene) filled by the conductive particles. When the silicon oil flows to the conductive layer of the silicon oil sensor, the conductive particles directly contact the silicon oil and become covered by the silicon oil. This causes a change in the electric resistance of the conductive layer, allowing for detection of leaked silicon oil is leaked based on the change of the electric resistance of the conductive layer.
While the conventional silicon oil sensor can detect certain types of silicon oil leaks, it suffers from a number of disadvantages.
For example, when the conductive particles are covered by the leaked silicon oil, the change of the electric resistance of the conductive layer is very slow and not significant. Thus, the conventional silicon oil sensor suffers from poor detection sensitivity and is unable to detect silicon oil leaks that occur slowly over time. As a result, the conventional silicon oil sensor is unable to reliably detect slow leaks, and thus provide warnings prior to power failure.
Additionally, the electric resistance of the conductive layer is also affected by other fluids, such as rain water. Thereby, when the conventional silicon oil sensor is used in an outdoor environment, a special film is often applied on the conductive layer to protect it from the rain water. The film is designed to permit the silicon oil to penetrate therethrough, however, such a film complicates the structure of the silicon oil sensor, adds a potential failure point, and increases the manufacturing cost.